[rotorwrench]

On Fords, the two brush should have a field terminal, an armature terminal, and a ground terminal. The 3-brush units will only have one terminal or just a wire exiting the body to connect to the cut out. A 2-brush unit should be using a 3-pole voltage regulator if it's an 8BA unit. With no voltage regulator, current limiter, and cut out poles the two brush will not be functioning as it should.

A generator can generally be converted to work as a 2-brush if it was a 3-brush by elimination of the 3rd brush and installation of the 2-brush type field coils. Some of the early two brush units have a 2-pole voltage regulator that has a dual purpose voltage regulator and current limiter in the same pole with a cut out next to it. These old dudes are getting harder to find these days. They usually have an armature wire and a field wire that protrude from the generator body so as to connect to the early style regulators.

The 3-brush is limited on output to around 20-amps and it puts out what ever amperage that the 3rd brush is set to. The battery regulated the voltage so they have to be well connected to a battery or they can get too hot. They lose efficiency when the rpm is increased so they aren't an ideal set up for a traveler that drives at night a lot.

Some folks have modified the 3-brush types with modern electronic current regulators. Some of these still use the 3rd brush and some don't. They still use the battery for voltage control but the current is switched on and off rapidly for control. They will reduce current output a lot when the battery is fully charged and pick up the load when the lights are turned on but they are still limited in their output capability.